It is well known that the driving speed of a vehicle can be measured by means of a stationary radar device and that a radar controlled indication device can be photographed together with the vehicle.
Because it, as a rule, is necessary to release monitoring pictures manually or by means of telecontrol, it is known that electromagnetic releasing means for the shutters exist.
Also, monitoring vehicles are used for traffic monitoring. From German Patent No. 1,139,315 it is known that the monitoring vehicle follows a vehicle with the same speed and prepares a documentary evidence of a vehicle exceeding the allowed speed by means of photographing the vehicle and the speedometer serving as vehicle speed indicator, together with photographically documenting the time and date.
From U.S. Pat. No. 3,206,748 a photographic traffic monitoring device is known, which is adapted to optionally determine the speed of a vehicle to be monitored by following it or by stationary operation by means of radar.
In the brochure TRAFFIPAX-micro speed of the company Traffipax-Vertrieb, Hildener Stra.beta.e 57, 4000 Dusseldorf 13, a traffic radar device is described, which likewise is adapted for mobile and stationary operation. The device is pivotable such that the traffic monitoring in the stationary operation can be achieved optionally from the left or the right side of the road. The traffic moving away or the approaching traffic can optionally be measured and photographically documented. In stationary operation, separately adjustable limit speeds are provided for passenger cars and motor lorries during monitoring the traffic moving away. The traffic radar device is adapted to be optionally mounted in patrol cars having fixedly mounted support for radar antenna or for mounting the radar antenna on a stand. In suitable vehicles the antenna can be mounted invisibly behind the grille and remain there during travel. For mobile operation the device is provided with an electronic speedometer having digital display. The speedometer is switched-on automatically as soon as the radar device is switched-off. Through corresponding signs at the prepared photo it can be seen whether the device has been operated with radar or with speedometer.
It is disadvantageous if the monitoring vehicle has to be driven with the same speed in the required proximity behind the vehicle to be detected, because it easily can be recognized as a police vehicle. In the brochure GATSO-meter of the company Gatsometer B.V., Tetterodeweg 10, 2050 AA Overveen, a device is mentioned, which likewise is adapted to be used in mobile or stationary operation. With this device it is furthermore possible to use the radar monitoring and the speedometer monitoring in a way that the monitoring vehicle is driven a at constant speed but more slowly than the vehicle to be detected. The speed of the monitoring vehicle and the relative speed, as measured by the radar device of the vehicle to be detected with respect to the speed of the monitoring vehicle, are reflected in a photographic picture of the vehicle to be detected.
In order to obtain evidence as irrefutable as possible, further data, e.g. date and time, are reflected in the picture.
The prior art traffic monitoring device of the above mentioned type, which is mounted in a monitoring vehicle and which serves to monitor the speed, is ineffective. On one hand, the monitoring vehicle has to be driven at constant speed and thus cannot be adapted to the given traffic. On the other hand, too many or too few pictures are taken, which means that vehicles driven too fast are possibly not detected and vehicles are photographed, which do not exceed the allowed speed. This is the case, for example, when the monitoring vehicle is, in fact, driven at constant speed but too fast. Exceeding the allowed speed is partly not recorded, because the radar device does not measure any exceeded speed. When the monitoring vehicle is driven too slowly, the device signals that the allowed speed was exceeded, which actually is not the case. The camera is released and a picture is taken, in which it later can be seen that the allowed speed.